This invention pertains to a gripper for a strapping machine. More particularly, this invention pertains to a gripper for use in the strapping head of a strapping machine for steel strapping material.
Strapping machines are well-known in the art. There are two principle types of strapping machines. One type of strapping machine positions and tensions a steel strap around a load to bundle or secure the load to, for example, a pallet.
A typical strapping machine includes a frame-like support for the overall machine, a working area to, for example, support a load, a strapping head, a chute around which the strap is fed and one or more dispensers for dispensing the strap material to the strapping head.
The strapping head pulls the strap material from the dispensers, and feeds it around the chute until a leading portion of the strap returns to the strapping head. At the strapping head, the leading portion or leading end is gripped and the trailing portion or end of the strap is retracted and tensioned to provide an appropriate compression on the strapped load. The strap is then sealed to itself in an overlapping manner, the trailing end portion is severed and the load removed from the machine.
The strapping head thus serves a number of functions. These functions and the general arrangements of strapping heads are provided in U.S. Pat. No. 4,791,968 to Pearson, U.S. Pat. No. 4,825,512 to Tremper et al. and U.S. Pat. No. 5,097,874 to Bobren. These patents, which are assigned to the assignee of the present invention, are all incorporated herein by reference. Two principle functions of the strapping head are to grip the leading end of the strap as it returns from around the chute and to seal the strap material to itself.
Strapping material is manufactured from a variety of materials in a variety of sizes. The ranges of sizes include both the width of the strap as well as the gauge or thickness of the strap.
In known strapping heads, the effectiveness of the gripper, that is that portion of the machine that grips the leading end of the strap while the strap is tensioned, sealed to itself and cut, is greatly dependent upon either or both the width and the gauge of the strap material. To this end, as strap material is changed, such as when a new source of strap material is supplied from a dispenser, adjustments must often be made to the gripper so that it can provide an appropriate force on the strap for the strapping head to properly carry out its remaining functions. In some known grippers, the strap is engaged at the strap edges. To this end, use of the gripper is almost wholly dependent upon the width of the strap material.
In other gripping arrangements, the gripper is dependent upon the gauge of the strap material and shim may be required at the gripper to compensate for strap gauge changes. Regardless of the type of gripper, consideration must be given to the force exerted on the strap so that the integrity of the strap is not compromised, such as by cutting into the strap material during gripping.
Moreover, attempts have been made to design strapping heads with gripper portions that can be separated from one another, such as on a pivotal frame, so that maintenance can be carried out on the strapping head. However, these attempts at design have been unsuccessful in designing an effective strapping head gripper in which the portions can separate from one another and which can accommodate varying gauges of strap material.
Accordingly, there exists a need for a gripper arrangement that can be mounted to a strapping head having pivotal portions for ready access to the strapping head, and which can accommodate varying gauges and widths of strapping material.
A strapping machine positions an associated strap material around an associated load and tensioning the strap material around the load. The strap for use with the machine has a width. The strapping machine includes a frame for supporting the load, a chute positioned on the frame for receiving the strap material and orienting the strap material around the load, and a strap supply.
A strapping head extracts the strap from the supply, feeds the strap through the chute around the load, passes the strap from the chute around the load, retracts and tensions the strap, and seals the strap to itself The strapping head includes a plurality of sealing elements and a gripper. The gripper grips and holds the strap material as it is tensioned and sealed to itself.
The gripper is positioned at an upstream location from the plurality of sealing elements. The gripper has a floating element and a stationary element. Each the floating and stationary elements includes a base surface. A plurality of teeth extend from one of the floating and stationary elements and a plurality of channels is formed in the other of the floating and stationary elements. In a preferred embodiment, the teeth extend from the stationary element and the channels are formed in the floating element.
Most preferably, each the floating and stationary elements is formed having a base portion or surface that defines a plane. In a preferred embodiment, the base surface planes are parallel to one another and are oriented at an angle of about 15 degrees relative to the pathway through the strapping head through which the strap material traverses. The teeth and channels are configured to secure the strap therebetween when the gripper is actuated such that when the gripper is actuated, the teeth, in conjunction with the channels, form substantially centrally located, localized deformations in the strap extending across a portion of the strap width.
Most preferably, the gripper assembly includes two teeth and two channels, with each tooth corresponding to a respective channel. The teeth include a gripping face formed at an angle of about 75 degrees (i.e., about 15 degrees from perpendicular) relative to the direction of travel of the strap through the strapping head.
Other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims.